1. Field of the Invention
The invention relates to a light emitting module, and more particularly to a light emitting module having high light-utilization efficiency.
2. Description of Related Art
FIG. 1A illustrates a schematic drawing according to a conventional backlight module. Referring to FIG. 1A, a backlight module 100 includes a light-guide plate 110, a light source 120, a diffuser 130, a bottom brightness enhancement film 140, and an upper brightness enhancement film 150. The light-guide plate 110 has a light receiving surface 112 and a light emitting surface 114. The light source 120 is located at a side of the light-guide plate 110 corresponding to the light receiving surface 112, and the diffuser 130 is located on the light emitting surface 114. In addition, the diffuser 130 is located between the bottom brightness enhancement film 140 and the light guide plate 110, and the bottom brightness enhancement film 140 is located between the upper brightness enhancement film 140 and the diffuser 130. The backlight module 100 is a side type design, and thus the light receiving surface 112 and the light emitting surface 114 are disposed adjacent to each other. Nevertheless, when the backlight module 100 is a direct type design, the light receiving surface 112 and the light emitting surface 114 are disposed opposite to each other.
Generally, the dispositions of the bottom brightness enhancement film 140 and the upper brightness enhancement film 150 are apt to render the emitted light concentrate to the regular view direction N, e.g. the normal direction of the light emitting surface 114 to provide satisfactory light emitting effect. The bottom brightness enhancement film 140 and the upper brightness enhancement film 150 are the optical films having prism structures, and the vertex angles of the prism structures are generally 90° to provide the desirable light emitting effect at the regular view direction N.
FIG. 1B schematically illustrates the optical effect of the conventional prism structures. Referring to FIG. 1B, the prism structure 160 is the surface structure design of the above-mentioned bottom brightness enhancement film 140 or the upper brightness enhancement film 150. In a normal circumstance, the light L1 is efficiently concentrated to the regular view direction N by passing the prism structure 160 to improve the light emitting effect at the regular view direction N. However, when the included angle θ between the light L1 and the regular view direction N is 0° to 10°, the light L1 is total inner reflected by the optical effect provided by the prism structure 160. Accordingly, the light L1 is unable to be emitted outward and be used such that the light utilization efficiency of the backlight module 100 is restricted.